Cement compositions may be used in a variety of subterranean operations. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a wellbore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the wellbore and the exterior surface of the pipe string disposed therein and/or between the pipe string and a larger conduit disposed in the wellbore. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the wellbore and may bond the exterior surface of the pipe string to the subterranean formation and/or the larger conduit. Among other things, the cement sheath surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like.
A broad variety of cement compositions have been used in subterranean cementing operations. In some instances, set-delayed cement compositions have been used. Set-delayed cement compositions are characterized by remaining in a pumpable fluid state for at least about one day (e.g., at least about 7 days, about 2 weeks, about 2 years or more) at room temperature (e.g., about 80° F.) in quiescent storage. When desired for use, the set-delayed cement compositions should be capable of being activated whereby reasonable compressive strengths are developed. For example, a cement set activator may be added to a set-delayed cement composition whereby the composition sets into a hardened mass. Among other things, the set-delayed cement composition may be suitable for use in wellbore applications, for example, where it is desired to prepare the cement composition in advance. This may allow, for example, the cement composition to be stored prior to its use. In addition, this may allow, for example, the cement composition to be prepared at a convenient location and then transported to the job site. Accordingly, capital expenditures may be reduced due to a reduction in the need for on-site bulk storage and high horsepower pumping equipment. This may be particularly useful for offshore cementing operations where space onboard the vessels may be limited.
While set-delayed cement compositions have been developed heretofore, challenges exist with their successful use in subterranean cementing operations. For example, set-delayed cement compositions comprising lime may not develop a high enough yield point to sufficiently suspend the solids in the slurry. The yield point is the threshold shear stress that must be applied to create flow of a fluid. Yield stress or yield point of cementing compositions directly affects their performance, especially related to stability, friction and mud removal. For example, if the slurry does not reach a specific yield point, the slurry solids may segregate, and the slurry becomes unusable. This is a greater issue in set-delayed cement compositions than in non-set-delayed cement compositions, because set-delayed cement compositions may need to suspend their solids for an extended period of time. Slurry rheology may be improved by the addition of water viscosifying suspension additives. However, these additives may be expensive and may be incompatible with some formulations of set-delayed cement compositions.